Spray coating is a facile deposition process with numerous existing and emerging applications. However,
spray coating is a stochastic process comprising impingement of many droplets which upon impact on a heated
substrate may dry or solidify individually or coalesce first to form a thin liquid film and then dry to yield a
thin solid film. There is very limited knowledge on how this process occurs; therefore in this work, high speed
imaging is used to visualize the spray coating process. Two model solutions including food-dye with properties
like those of water, and poly (3, 4-ethylenedioxythiophene) : poly (styrenesulfonate) (PEDOT:PSS), a polymeric
solution, are sprayed onto permeable glossy paper and regular impermeable glass substrates. Substrates are kept
at room temperature and 80 ?C elevated temperature. In some cases, a vertical ultrasonic vibration is imposed
on the substrate to study its effect on the coating process. It is observed that the spray coating process is highly
random and stochastic. A higher substrate temperature results in a better coating process in that a more uniform
and defect-free coating forms. Imposed vibration in the case of glossy paper substrates results in better droplet
spreading and more uniform coating. The results also show that under the conditions of these experiments,
impinged droplets dry individually or as islands of multiple coalesced droplets to form a coating. In other words,
at used spray flow rate and spray droplet size, a continuous thin liquid film does not form prior to drying even
at room temperature. Further systematic studies and high magnification lenses are required to visualize and
understand the details of the process.
HUANG Jianchi (黄渐持), YUAN Zhihao (袁志豪), GAO Siyi (高思易),LIAO Jianshan (廖健杉), ESLAMIAN Morteza*
. Understanding Spray Coating Process: Visual Observation of Impingement of Multiple Droplets on a Substrate[J]. Journal of Shanghai Jiaotong University(Science), 2018
, 23(1)
: 97
-105
.
DOI: 10.1007/s12204-018-1914-0
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